This invention relates to a storage medium, such as an IC memory chip and an IC memory card, for storing map information for a navigation system, and also relates to a map information-offering system using such a map information storage medium.
A navigation system disclosed in Japanese Laid-Open Patent Application No. 4-60416 uses a CD-ROM as a map information storage medium. The CD-ROM has a large memory capacity, and therefore map information covering a wide range can be written onto it; however, generally, the read rate (read speed) of the CD-ROM is low. In this navigation system, the map information in the CD-ROM is divided into many regions, and map information of one region at which a vehicle is located at present is stored in another memory, and the navigation is carried out in accordance with the map information stored in this memory, thereby increasing the read rate. However, an expensive reader for reading the map information from the CD-ROM is required.
A navigation system disclosed in Japanese Laid-Open Patent Application No. 3-77200 uses an IC memory card as a map information storage medium. The read rate of the IC memory card is high, and a reader for the IC memory card is relatively inexpensive. However, the IC memory card has a small memory capacity, and therefore can only store map information covering a narrow range. Therefore, when the distance from a starting point to a destination is long, the optimum route can not beforehand be computed, and therefore the navigation along such optimum route can not be effected. Namely, when the distance from the starting point to the destination is long, it is only possible to provide a simple navigation in which the map information from the IC memory card is displayed, with the present position of the vehicle indicated on this displayed map information. And besides, in this navigation system, many IC memory cards, corresponding respectively to many regions located along the route of the vehicle, must be sequentially inserted into and removed from a slot portion of the navigation system. This provides a burden on the driver.